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<TITLE>Font-formats recognized by the Linux kbd package: CPI fonts</TITLE>
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Contents
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In the DOS world screen or printer fonts come in
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Code Page Information format. There are two versions:
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the MS-DOS/PC-DOS "FONT" format, and the DR-DOS/Novell DOS
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"DRFONT" compressed format.
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These *.CPI files may contain fonts for several
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code pages, and, given a code page, for several point sizes.
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MS-DOS files usually have 16x8, 14x8, 8x8 fonts, while
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DR-DOS files often have 6x8, 8x8, 14x8, 16x8 fonts (in this order).
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Printer .CPI files have only one font.
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(One sometimes encounters entirely different .cpi files,
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namely Unix .cpio files moved to a DOS machine with 8.3 filenames.
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Such files are archives.)
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The files in "FONT" format have the following layout.
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First a 23-byte header.
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struct {
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char id0; /* 0: 0xff */
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char id[7]; /* 1-7: "FONT " */
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char reserved[8]; /* 8-15: 0 */
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short pnum; /* 16-17: number of pointers: 1 */
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char ptyp; /* 18: type of pointers: 1 */
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long fih_offset; /* 19-22: file offset of FontInfoHeader: 0x17 */
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} FontFileHeader; /* 0-22 */
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(Files in "DRFONT compressed format" have 0x7f "DRFONT " in bytes 0-7.
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After this FontFileHeader they have an extended header
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struct {
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char num_fonts_per_codepage; /* 23: N=4 */
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char font_height[N]; /* 24-27: height of each font */
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long dfd_offset[N]; /* 28-43: file offsets of DisplayFontData */
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} DRDOSExtendedFontFileHeader;
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and consequently fih_offset will be 44 (0x2c) instead of 23 (0x17).)
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Next a 2-byte header that tells how many code pages this file contains.
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struct {
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short num_codepages;
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} FontInfoHeader; /* 23-24 */
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Next the indicated number of code pages.
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Each code page has a header and font data. In some files all headers
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come first and then all font data. In other files headers and font data
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alternate, that is, data for one code page is kept together.
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The code page header (the offsets given are for the first occurrence):
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struct {
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short cpeh_size; /* 25-26: size of this header: 28 */
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long next_cpeh_offset; /* 27-30: offset of next header; 0 or -1 for last */
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short device_type; /* 31-32: 1: screen, 2: printer */
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char device_name[8]; /* 33-40: e.g. "EGA " */
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short codepage; /* 41-42: 0, 437, 737, 85[0257], 86[013569], ... */
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char reserved[6]; /* 43-48: 0 */
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long cpih_offset; /* 49-52: pointer to CPInfoHeader or 0 */
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} CPEntryHeader; /* 25-52 */
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MS-DOS and PC-DOS sometimes have 26 instead of 28 for the cpeh_size
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field in printer font files; one even meets both 26 and 28 in the same file.
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Probably there is confusion over whether cpih_offset
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is short or long.
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When headers and fonts are interspersed, next_cpeh_offset
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will point past the font, regardless of whether more entries follow.
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When first all headers are given, next_cpeh_offset is zero
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in the last header.
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It happens that next_cpeh_offset does not point to the
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next header, but to the one after that, or that it is zero while
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still one header follows. In such cases num_codepages
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gives the correct number of headers. (In the cases where it is
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zero while still one header follows, the last header is a dummy
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one, for codepage 0 and with no associated font.)
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Early DR-DOS printer font files have 1 instead of 2 in device_type.
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Device names include "EGA ", "LCD " for screen, and
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"4201 ", "4208 ", "5202 ", "1050 ", "EPS ", "PPDS "
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for printer devices.
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A code page font starts with a general header:
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struct {
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short version; /* 53-54: 1: FONT, 2: DRFONT */
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short num_fonts; /* 55-56 */
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short size; /* 57-58: length of font data for each font */
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} CPInfoHeader; /* 53-58 */
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(For printer fonts num_fonts is 1 or 2, while only a single
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font follows. For screen fonts num_fonts is 1, 3 or 4.
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DRFONT files have in the size field the size (24) of the
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DRFONT header without the index table.)
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And then for each font a header followed by the actual data.
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For screen fonts
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struct {
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char height; /* 59: one of 6, 8, 14, 16 */
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char width; /* 60: 8 */
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short reserved; /* 61-62: 0 */
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short num_chars; /* 63-64: 256 */
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} ScreenFontHeader; /* 59-64 */
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and for printer fonts
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struct {
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short printer_type; /* 59-60: 1=4201/1050/EPS, 2=5202/4208/PPDS */
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short seqlength; /* 61-62: length of escape sequences */
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} PrinterFontHeader; /* 59-62 */
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followed by two escape sequences of the indicated length
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to select the hardware codepage or the downloaded codepage.
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However, in DRFONT files the CPInfoHeader is followed by
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the DRFONT header, consisting first of 4 ScreenFontHeaders,
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one for each point size, and then an index indicating where
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in the font bitmap the corresponding characters can be found.
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struct {
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struct ScreenFontHeader sfh[4];
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short FontIndex[256];
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} DRFONTheader;
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The font index is some integer, in the range 0-400 or so,
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indicating where in the font this code position can be found.
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In this way the font data is separated from the code used.
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Linux does not accept .CPI files, but the codepage
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utility from the kbd package is willing to read .CPI files
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of "FONT" type, and output .cp files suitable for setfont.
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For example, the call codepage -a iso.cpi will create
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ten font files 850.cp, 437.cp, ..., 869.cp
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each containing a single font of pointsize 16, and
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codepage -a ega2.cpi six font files
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850.cp, ..., 737.cp each containing three fonts
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of pointsizes 8, 14, 16.
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Next
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Contents
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